The objective of the proposed work is to investigate the relationship between cell proliferation and neoplastic competence of perinatal lung tissue. Physiologic peaks of Type 2 cell proliferation will be determined using a combination of morphometric and autoradiographic techniques. Exposure of high and low Type 2 cell proliferation, and the number of lung tumors obtained during the different periods compared. BIBLIOGRAPHIC REFERENCE: Kauffman, S.L. (1975) Kinetics of Pulmonary Epithelial Proliferation during Prenatal growth of the Mouse Lung. Anat. Rec. 183:393-404.